<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
   <script>
       var a = 12;
       var b = null;
       console.log("a="+a);
       console.log("b="+b);
       var c = true;
       var d = false;
       console.log("c="+c);
       console.log("d="+d);
   </script>
</body>
</html>